In the telephone industry in recent years, it has become highly desirable to be able to quickly and easily, from the central office, disconnect a selected subscriber's equipment to determine whether or not a reported fault may be in the line between the office and the subscriber's station, or whether the fault may lie in subscriber's equipment. The reason for this is that when a fault is reported, generally by a subscriber, it may lie anywhere between the central office up to and including the subscriber's equipment. Before sending a repairman to a subscriber's location, a quick check could eliminate costly service calls if the fault is in the lines.
This problem is complicated with the recent increase in situations where the subscriber equipment is not owned by the telephone company, and the telephone company will not be recompensed if the fault lies in the subscriber's equipment itself.
Previous attempts to provide apparatus for quickly and easily disconnecting subscriber equipment from the telephone lines have generally all adopted an approach whereby the switching network is operated or activated responsive to a capacitive or voltage buildup. To effect the disconnect in such approaches, the telephone company applies a relatively large voltage to charge a capacitor or battery. When the charge rises to a prescribed level, a trigger or switch begins the discharge of the capacitor or battery through a relay. Operation of the relay to a second stage causes the customer's equipment to be disconnected. The normal condition is restored by applying a voltage of opposite polarity to reverse the status of the relay. Such an approach has several disadvantages. First, capacitors of the size contemplated are not reliable in that they tend to fail or have a short life. Secondly, such networks generally draw a small amount of current continuously, even when not in a test stage. Thirdly, such an approach is relatively slow-acting in that it requires approximately two seconds charge time and seventeen seconds discharge time. As a result the customer's phone is out of service for times up to approximately thirty seconds.
In the instant approach, the solution to the problem set forth above is approached by applying a line potential directly to a switching network to initiate the switching action. No capacitive or voltage buildup is necessary, and the network operates in a very short time span (on the order of milliseconds).
In general, the approach of the present invention is to apply a disconnect signal on at least one of the tip and ring lines (preferably both) which directly operates a first switching means to substantially immediately disconnect the selected one or both of the tip and ring lines from the subscriber equipment and to simultaneously connect the selected tip and/or ring line to ground through a prescribed resistance selected to be indicative of a line continuity. A second switching means operates directly responsive to the re-establishment of the normal voltage on the lines for immediately restoring the normal condition. The switching means contemplated in the present invention is a latching relay which is operated by a transistor, which in turn is activated by the receipt of the signal voltage. The relay contacts serve to disconnect the normal line condition and connect the signal voltage to ground through a relatively large resistance. When the central office sees in its equipment that its signal is connected to ground, it is then known that the lines are operative as intended, and the proper service personnel can be dispatched to correct the fault.
It is therefore an object of the present invention to provide an improved telephone line/subscriber equipment disconnect apparatus.
It is another object of the present invention to provide a disconnect apparatus of the type described which utilizes no capacitive or voltage charge/discharge to effect the switching action.
It is another object of the present invention to provide a disconnect apparatus of the type described which is electrically disconnected from the telephone lines during normal operations, so that no current is drained therefrom unless and until the switching action is instituted.
Other objects and a fuller understanding of the invention will become apparent upon reading the following detailed description of a preferred embodiment along with the accompanying drawing.